1. Field of the Invention
The present invention relates to a method of fabricating polysilicon film by Nickel (Ni) and Copper (Cu) induced lateral crystallization, particularly to process under low-temperature annealing condition being about 10 times faster than that induced by Ni alone while keeping the similar grain size. Therefore, this invention substantially reduces the processing time, thereby increasing the industrial applicability adopting the method.
2. Discussion of the Related Art
At present the hydrogenated armophous silicon (a-Si:H) thin film was applied to various areas, i.e., the solar battery in calculators; the thin film transistor (TFT) as a switching element in a active matrix liquid crystal display (AMLCD). AMLCDs have been used in notebook computer and digital camera and gradually replaced the conventional cathode ray tube (CRT) in monitors and desktop computers. However, the field effect mobility of a-Si:H is low, i.e., xcx9c0.5 cm2/V-sec, which limits its performance. A polysilicon TFT is able to provide higher field effect mobility, i.e.,  greater than 50cm2/V-sec, and reduce the response time of display than that of an amorphous silicon TFT. Traditionally, there are three ways to grow low temperature polysilicon thin film.
(a) direct growth of polysilicon thin film by high-temperature heat treatment,
(b) conversion of an amorphous silicon (a-Si:H) thin film to polysilicon by Ni induced crystallization,
(c) conversion of an amorphous silicon (a-Si:H) thin film to polysilicon by excimer laser annealing.
In (a), a polysilicon thin film can be grown by low pressure chemical vapor deposition (LPCVD) at a temperature above 600xc2x0 C. Since the glass substrate of LCD becomes soft at temperature higher than 600xc2x0 C., an expensive quartz substrate must be used, thereby increasing the fabrication cost.
In (b), the amorphous silicon (a-Si:H) film was first deposited on glass substrate by plasma enhanced chemical vapor deposition (PECVD) or LPCVD. Ni is deposited either on or under the amorphous silicon (a-Si:H) film. Then that was annealed at a temperature below 600xc2x0 C. to crystallize a-Si:H. When that was annealed at 550xc2x0 C. for 20 h, the range of crystallization is about 30 xcexcm from the edge of Ni bars and the growth rate of polysilicon is 1.5 xcexcm per hour. If the annealing time is shorter, the growth rate increases to about 2 xcexcm per hour, This method requires a long processing time, causes difficulties in mass production. The use of Cu improves the growth rate of polysilicon, i.e., approximately 4 to 10 times larger than that of Ni induced polysilicon, but the grain size is 10 times smaller, it is difficult to achieve high field effect mobility and reduce the response time of LCD.
In (c), the amorphous silicon (a-Si:H) film was first deposited on glass substrate by PECVD or LPCVD. then excimer laser was used to anneal the a-Si:H film to form polysilicon crystallization. Although the process time decreases but the grain size is smaller, the electrical characteristic of the TFT is worse than that of Ni induced polysilicon.
Accordingly, the present invention is directed to a method of fabricating polysilicon film that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
The main object of present invention is to provide a method of fabricating polysilicon film which improves the growth rate of polysilicon thin film by mean of applying low-temperature annealing to hydrogenated amorphous silicon (a-Si:H) thin film.
Another object of the present invention is to provide a fabrication method for a polysilicon film having reliable electrical characteristics.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the present invention includes the steps:
a) evaporating a 1-nm to 50-nm-thick Copper (Cu) on substrate;
b) evaporating a 1-nm to 50-nm-thick Nickel (Ni) on said Copper (Cu);
c) forming a 1-nm to 200-nm-thick amorphous silicon thin film on thereof obtained according to b) including the Copper (Cu) and Nickel (Ni): and
d) forming a polysilicon thin film on thereof obtained according to c) by below 600xc2x0 C. annealing.
Also, the present invention includes a fabrication method for polysilicon film comprising the faster growth rate of polysilicon thin film under below 600xc2x0 C. annealing condition, i.e., this invention substantially reduces the processing time, thereby increasing the industrial applicability adopting said method.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.